Many of the known heat treating furnaces have a hot zone with a circular cross section. A circular cross section hot zone, however, unnecessarily limits the maximum size workpiece load that the heat treating furnace can accommodate. During operation of the known heat treating furnaces, workpieces, furnace components, or in the case of a brazing furnace, the brazing alloy, can drop onto the hot zone floor causing damage thereto. Hitherto, the hot zone enclosure had to be removed in entirety from the furnace pressure vessel in order to repair or replace the hot zone floor. Such a laborious process leaves much to be desired.
There are several known designs for electric heating elements and their associated supports used in electric heat treating furnaces. A problem with the known designs is that they are prone to shorting out because the surfaces of the electrically insulated components of the heating element supports are progressively metallized during heat treating cycles.
Many of the known heating element supports include a stand-off or support shaft that threads into the hot zone enclosure. Such a heating element support is subject to distortion and galling from thermal cycling in the furnace. This distortion and galling causes the threaded portion of the stand-off to seize, which makes the heating element support very difficult to remove.
Another drawback of the known heating element supports is that they must be specifically designed for either graphite or metal heating elements. A graphite heating element is significantly thicker than a metal heating element. Furthermore, the known heating element supports must also be uniquely designed to accommodate different types and/or thicknesses of heat shielding or insulation that is used to line the furnace hot zone enclosure. Still further, the known heating element supports provide little, if any, adjustability for controlling the distance of the heating element from the heat shield.
Gas injection nozzles are used in heat treating furnaces to distribute a cooling gas over the workpiece load during the cooling portion of a heat treating cycle. The known designs for gas injection nozzles include a tube having flared ends which is formed of rolled molybdenum sheet metal. Such a design is disclosed in U.S. Pat. No. 4,560,348, assigned to Abar Ipsen Industries, Inc., the assignee of the present application. Another design employs a threaded graphite tube as described in U.S. Pat. No. 4,765,068. The sheet metal tube design can easily become dislodged during operation of the heat treating furnace. Furthermore, such a nozzle becomes brittle after exposure to several heat treating cycles. The threaded graphite tube has limited utility because it can contaminate the workpieces with carbon during some heat treating processes.
In view of the foregoing, it would be very desirable to have an electric heat treating furnace which overcomes the disadvantages of the known heat treating furnaces.